Subaru tuners and car owners have been fooling around with turbos for decades now, with lots of choice for Sti and WRX engines, but the industry-wide interest in turbos isn't driven by hot rod guys, but bean counters, both government and the big car companies.
Mileage mandates have forced the big guys, like Porsche, Ford, and others, to shrink block size but up HP by adding one or more turbos. Performance is a by-product, not the goal. Porsche went from 3.8 to 3.0 liters in their latest 911, but added twin turbos, while Ford went to a V-6 with turbo from a V-8 in their F-150, with no decrease in HP. In that manner, they produce more efficient engines, without lowering HP. Of course, the fuel savings are illusory if you put your foot in it, as most of us are prone to do.
IAG, a high-performance Subaru engine builder, now manufactures a 4-cylinder, 2.5 liter billet block for Subaru that will take up to 1500 HP. Cost is about $14,000. Warning: stay away from their website, Stan, far away!